Combustion engines in most vehicles rely on reciprocating poppet valves, which open and close at precise moments to either allow fuel mixture into an engine's cylinder or allows spent gases to escape. These control valves are typically spring-loaded by a valve spring for automatic return into the closed position and are stressed between a reference support structure of the valve, generally a cylinder head, and a valve spring plate or spring retainer axially held to the valve stem. Specially shaped holding keepers (also referred to as keys or collets) are mounted between a suitable surface in the spring retainer and annular, mating grooves on the valve stem, connecting the valve member to the spring.